CELL-CONTEXTS AND FORMS OF CELLS. 185 



momum, coca, eucalyptus, frangula, gelsemium, granatum, hama- 

 melis, hyoscyamus, Jamaica quassia, krameria, pimenta, Prunus 

 serotitta, quercus, quillaja, rhamnus purshianus, senna, uva-ursi, 

 vanilla, viburnum prunifolium, and Xanthoxylum. 



III. ROSETTE AGGREGATES of calcium oxalate consist of numer- 

 ous small prisms and pyramids, or hemihedral crystals more or 

 less regularly arranged around a central axis, and have the appear- 



FIG. 106. Tetragonal crystals of calcium oxalate: A, a to f, crystals from the 

 leaves of the onion (Allium Cepa) ; B, a to g, crystals from the stem of Trades- 

 cantia viridis. After Dippel in "Das Mikroskop." 



ance of a rosette or star (Fig. 107, A). The development of 

 these aggregates may be readily observed in the stem of Datura 

 Stramonium. Crystals of this class are more widely distributed 

 than any of the others, and are characteristic of a number of drugs. 

 Clustered crystals in the form of rosette aggregates occur in 

 numerous drugs, as follows: Althaea, anisum, buchu, calendula, 

 cannabis indica, carum, caryophyllus, castanea, chimaphila, conium, 

 coriandrum, cusso, eriodictyon, euonymus, foeniculum, frangula,, 

 galla, geranium, gossypii ortex, granatum, humulus, jalapa, pilo- 



